Welcome, Grace.
I think Moira asks an important question. Do your kids act this way only toward you, or toward others? Could it be they are just doing this with you (because they have that modeled by dad, or because you are mom)?
I also see that kids of all ages behave differently with mom than anyone in the world. Starting with toddlerhood. Mom is safe, so they save up all the crap they have been dealing with all day and let it out on mom!!
Dr. Anthony Wolf describes this perfectly in his book on teenagers (the second toddlerhood in my opinion): "Get out of my Life...but first could you drive me an Cheryl to the mall". (yup, that's the name of the book...great book, not all humorous...)
He thinks that how kids behave with their parents is NOT a good indicator of how they are as people....as they will not spend their lives with the parents.
I see this as a teacher: kids who are awesome students, funny and kind, and they are horrible with their parents. Ok, not horrible, but certainly not how they are toward me or their peers in school.
But I understand your children are not adolescents. Perhaps the same dynamic is at work?
I will admit I occassionally worry about this same thing with my teenagers. I know the operative word is "teenager" but on occassion, I see tendencies for them to be like their N father. Then the feeling passes and I realize that they are not always like that, they are just expressing negative feelings in a genetic manner (facial expressions like dad, etc) and perhaps some of what they do has to come from what they see dad do (environmental). My leaving that abusive relationship, though, was a real boost for them in the "how to treat people" department....;
All in all, they are young, and although my ex never progressed emotionally past adolescence, they most likely will (they are already much nicer people).
Whatever you conclude, I hope you will not "blame" yourself for your children's lives and how they relate to people. It's their path, and although you did what you could...beyond a certain point, they are responsible for their own lives.
And you CAN set boundaries with grown children. My friend had to call the police on her angry/abusive adult son, so I know the implications can be extreme. But he same "rules" apply to adult children as smaller ones: "Mom will not accept that language/demeaning talk (whatever) from anyone. When you are ready to discuss this respectfully, let me know.. I am .....(going, leaving the room, going to Europe, calling the cops..whatever......). Decide what YOU will and will not accept from anyone in your life, and let others (kids included) decide for themselves once they know your boundaries.
Bless you, I know how kids can wrench our hearts (they occupy so much space in there!!).